Pressure-responding microphones have occasionally been placed on rigid boundaries for recording purposes, and indeed there is merit in this idea. A new type of microphone, called the "pressure zone microphone," has recently been introduced for this purpose. This microphone obscures the diaphragm from receiving any direct sound by pointing it towards the rigid boundary, in the mistaken belief that, were it pointing forwards, it would display the on-axis high-frequency rise characteristic of such microphones when used free-field. It is shown that this is not true and that for a given capsule size, the frequency and polar responses are significantly degraded by obscuring the diaphragm. Conversely, for a given frequency and polar response tolerance, a larger diaphragm, giving lower self-noise, could be used for a non-occluded design. We present both experimental data and a theoretical model to verify our contentions.
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